The present invention is directed generally to an apparatus and method for removal of ash and slag from steam generator tubing and more particularly to such an apparatus and method which utilizes an explosive blastwave and sandblast-like effect created by the detonation of high velocity detonating cord configured in multi-directional loop clusters and suspended between alternating banks of boiler tubing.
It is well known that in the operation of a steam generator, ash and slag build up on the tubes or heat transfer surfaces through the combustion of coal. As this ash and slag accumulates, a great deal of heat loss occurs which greatly impairs the efficiency of the boiler and its ability to produce electricity. Maintenance procedures designed to remove these deposits have met with mixed results. The techniques of manual shaking, hand rodding, high pressure water and shotgun blasting are still utilized in steam generators today. However, shortcomings such as risks to personnel and consumption of time have made these methods less appealing. It was not until the introduction of high explosive tube cleaning that adequate removal of ash and slag could be accomplished quickly while personnel were safely outside of the boiler.
High explosive deslagging is not without its drawbacks. A stick of dynamite, for example, used against hard slag may only clean a small percentage of one tube assembly. Several sticks of dynamite may not be linked together due to the massive overpressure that this would create within the boiler. In addition, boiler tube assemblies are spaced very close together in some areas and the tube wall construction is very thin and may not withstand a dynamite charge without damage.
High explosive detonating cord has been used for many years to remove one surface from another, thus the logical progression to detonating cord. Detonating cord such as Pentaerythrite Tetranitrate (PETN) is virtually the only commercial high explosive available that is packaged to allow detonation coverage of several square yards with the explosive weight of only a few sticks of dynamite.
One such method employing the use of detonating cord in a steam generator is described in the Halliburton/Jet Research Center, U.S. Pat. No. 5,056,587. This method relies on a sequential series of explosively induced tube vibrations to separate the ash and slag from boiler tubing. The procedure describes critical placement of the detonating cord in a substantially vertical position on each tubing panel immediately adjacent to the exterior surface of the tubes. It further suggests placement of said cord a distance of about twelve inches from tube spacers to avoid dissipation of explosive energy.
Vibrational cleaning methods are problematic due to the fact that boiler tube hangers and spacers add a great deal of rigidity to each assembly. When ash and slag deposits build up between the tubes, this bridging of ash greatly exacerbates the problem. Vertical hanging tubes that normally swing freely are often anchored at the bottom in a bed of ash, and tube assemblies with several feet of individual tubes often appear as a solid wall of ash. Since tube spacers and hangers protrude from the tube assemblies, they are usually one of the first places where ash deposits are likely to form and must be cleaned as well.
Accordingly, a primary object of the invention is to provide an improved apparatus and method of deslagging a boiler from utilizing an explosive blastwave and kinetic energy.
Another object of the invention is to efficiently remove substantially all of the ash from steam generator tubing with explosives and without damage to the tubing.
Another object of the invention is to create a high explosive blastwave in all directions to remove ash and slag from steam generator tubing.
Another object of the invention is to effectively harness the kinetic energy imparted by an explosive blastwave to further remove ash from adjacent steam generator tubing.
Another object of the invention is to provide an apparatus and method of deslagging a boiler with a minimum number of personnel and without danger to said personnel.
Another object of the invention is to provide an improved apparatus and method of deslagging a boiler which effectively removes ash and slag from tube hangers and spacers as well as from the boiler tubes themselves.
Another object of the invention is to provide an improved apparatus and method of deslagging a boiler without water so that clean up of dry ash and slag is facilitated.
Finally, a further object of the invention is to provide an improved apparatus and method of deslagging a boiler which are simple, efficient and economical.